Low impurity hydrazine

ABSTRACT

PURIFICATION OF AQUEOUS SOLUTIONS OF HYDRAZINE AND LOWER ALKYL HYDRAZINES BY THE REMOVAL OF SODIUM AND OTHER CATIONS, CHLORIDE, CARBONATE AND OTHER ANIONS FROM AQUEOUS SOLUTIONS OF SUCH HYDRAZINES. THE PRODUCT SOLUTIONS HAVE, AT MOST, EXTREMELY LOW LIMITS OF IONIC IMPURITIES.

United States Patent "ice US. Cl. 423-407 6 Claims ABS CT OF THEDESCLOSURE Purification of aqueous solutions of hydrazine and loweralkyl hydrazines by the removal of sodium and other cations, chloride,carbonate and other anions from aqueous solutions of such hydrazines.The product solutions have, at most, extremely low limits of ionicimpurities.

This is a continuation-in-part of co-pending Ser. No. 881,589 filed Dec.2, 1969, now US. Pat. 3,652,218, issued Mar. 28, 1972.

The commonly used Raschig synthesis of hydrazines reacts aqueous sodiumhypochlorite with aqueous ammonia to form chloramine which reactsfurther with ammonia to form hydrazine according to Equations 1 and 2:

\Nhen primary or secondary lower alkyl amines are substituted forammonia in Equation 2, the corresponding lower alkyl substitutedhydrazines result.

In addition to synthesis reactions 1 and 2, side reactions occur to someextent as represented by Equations 3 and 4:

By-product sodium chloride is formed according to Equation 2 in a 1:1molar ratio with the desired hydrazine product and ammonium chloride isformed in lesser proportions according to Equations 3 and 4. Thesechlorides and any other relatively non-volatile by-products are removedby flashing the more volatile hydrazine and water from the relativelynon-volatile by-products.

The hydrazines are concentrated and refined by distillation and/ orextraction.

In spite of these process operations, aqueous hydrazine solutions,containing up to 65 percent of N H the N H -H O hydrate, still containminor amounts of ionic impurities, particularly sodium chloride. Theseamounts, in parts per million (p.p.m.), are not of consequence for manyuses of hydrazine but they are objectionable for certain uses, forexample, in electroplating and in nuclear-powered electric generatingplants. For these and other purposes, it is required that aqueoushydrazine solutions be provided which contain preferably Zero ppm. NaClor, at least, below ppm.

One object of this invention is to provide a method for the purificationof aqueous solutions of hydrazines. More particularly, an object of thisinvention is to provide a method for the removal therefrom of thesesmall amounts of ionic impurities. A further object is to providepurified aqueous hydrazine uniquely suitable for certain uses. Other andfurther objects appear in the following description.

The objects of this invention are achieved by contacting 3,740,436Patented June 19, 1973 the aqueous hydrazine solution in one step withthe hydrazinium form of strongly acidic cation exchange resins and inanother step with the hydroxyl form of strongly basic anion exchangeresins and separating the treated aqueous hydrazine from the resins. Ina further embodiment of the invention, cyclic treatment of aqueoushydrazine solutions is contemplated in which a plurality of bodies ofthe cation and anion exchange resins are alternately used andregenerated to provide continuous treatment of the hydrazine solutionswith or without automatic control of the treating and regeneratingportions of the cycle.

In the process of the invention the cation exchange resin is used ineither the first or second step, preceded or followed by the use of theanion exchange resin. Equally satisfactory results are obtained byeither procedure.

It is known, for example, in US. Pat. 2,789,036 to remove anions such aschlorate, sulfate, chloride and ferrite from aqueous caustic soda bycontacting the canstic solution with an anion exchange resin. US. Pat.2,991,- 156 discloses removing iron from aqueous caustic soda bycontacting the certain polyvinylbenzyl sulfonium halide resins. Glycerolhas been purified by passage through successive beds of regeneratedcation and anion exchange resins as described in Ind. Eng. Chem., vol.43, pp. 1065- 70 (1951). In addition, hydrazines have been purified asdescribed in US. Pat. 3,458,283 by exchanging hydrazinium salt solutionswith a cation exchange resin to adsorb hydrazinium ions on said resinand recovering the purified hydrazine by eluting the hydrazinium resinwith aqueous caustic soda. It appears that great care would be requiredin this patented process to use exactly the stoichiometric quantity ofcaustic soda and to contact all of the hydrazinium resin with all of theaqueous caustic soda allowing ample time for complete interaction sinceany excess of the caustic soda or any unreacted caustic soda used in theelution must contaminate the product with ionic impurities.

Aqueous hydrazines are strongly basic and are strong reducing agentswhich interact with many ion exchange resins. Some of the resins aredegraded, substantially inactivated or rendered inoperative by suchinteraction. For example, aqueous hydrazine, reacting with the hydrogenform of active cation exchange resins, generates quantities of heat.Proper design and control is required to dissipate such heat to preventmelting certain resins. Other problems arise which are solved by theprocess of the present invention.

In operation, fresh or acid-regenerated cation exchange resin is firstconverted to the hydrazinium form of resin under conditions providingdissipation of heat at an adequate rate to avoid damaging the resin.With certain resins, this operation is suitably performed in the toweror container for holding the bed of resin as it is to be used inde-cationizing the aqueous hydrazine depending on ambient air todissipate the heat liberated. In other instances, this preliminarytreatment is suitably carried out in a separate vessel equipped withjackets and/ or cooling coils to remove the heat. Similarly,regeneration of the exhausted or partly spent resin with acid requiressuitable provision for heat control.

The strongly basic anion exchange resins suitable for use according tothe present invention are usually initially in the hydroxyl form but, ifnot, they are converted to the hydroxyl form by treatment with aqueousalkali, preferably caustic soda. The spent or partially exhausted resinsare also regenerated with aqueous caustic soda. Siutable precautions aretaken to dissipate the heat liberated in both of these processes.

In continuous operation, the aqueous hydrazine flows through a bed ofthe cation exchange resin initially in the hydrazinium form and thenthrough a bed of the anion exchange resin initially in the hydroxylform. Alternatively, the aqueous hydrazine flows through a bed of theanion exchange resin initially in the hydroxyl form and then through abed of the cation exchange resin initially in the hydrazinium form. Whenthe resin beds are partially spent and passage of ions through the bedsis imminent, the flow of aqueous hydrazine is switched to a parallelpair of towers and flows through beds of regenerated resins. While theaqueous hydrazine is flowing through the second pair of towers, theresins in the first pair of towers is suitably regenerated. The cationexchange resin bed is washed by flowing soft or deionized water throughit to remove aqueous hydrazine, then aqueous acid, preferablyhydrochloric acid, about 1 to 10 percent HCl is passed through the beduntil cations other than hydrogen are substantially removed and thenwater is again passed through the bed until chloride ions aresubstantially removed. Similarly, the anion exchange resin bed isregenerated by flowing soft or deionized water therethrough to removeaqueous hydrazine, then aqueous alkali, preferably caustic soda, about 1to 10 percent is passed through the bed until anions other than hydroxylare substantially removed and then water is again passed through the beduntil sodium ions are substantially removed. The regenerated beds aresuitably covered with soft or deionized water until used. The aqueoushydrazine washed from both beds is recycled to storage of impurehydrazine for further treatment or, if too dilute, to the hydrazineplant for concentration.

The reactions involved in the process of the present invention,including regeneration reactions, using R nonstoichiometrically torepresent the resins, are as follows:

Cation exchange resin Pretreatment:

R.H+N H R.N H Deionization:

R.N H +Na+-+R.Na+N H +H+ Regeneration:

R.Na+*HCl- R.*H+NaCl Anion exchange resin Pretreatment:

R.Cl+NaOH R.-OI-I+NaCl Deionization:

R.OH+Cl"-+R.Cl-]-OH Regeneration:

The process of this invention is useful in purifying aqueous solutionsof hydrazine and of lower alkyl hyhydrazines having 1 to 4 carbons peralkyl group and from 1 to 2 alkyl groups per nitrogen, whether made bythe Raschig process or otherwise. Examples of such alkyl substitutedhydrazines include monomethylhydrazine, unsdimethylhydrazine,sym-dimethylhydrazine, ethylhydrazine, ios-propylhydrazine, secondaryand tertiary butylhydrazine.

In the deionization operations according to the present invention,temperatures at which fusion, deactivation or damage to the resinsoccurs are to be avoided. Generally, temperatures are maintained below300 F. to avoid damage to the resins. A hot process stream of aqueoushydrazine to be deionized is appropriately cooled as necessary to avoiddamage to the resin. Otherwise, temperatures of operation are notcritical and are suitably as low as zero F.

Besides sodium and chloride ions, minor amounts of other cations andanions are effectively removed by the process of the present invention.In the product, lithium, potassium, copper, iron, chromium, calcium,barium and strontium cations, if present, are reduced to negligibleamounts. Similarly, carbonate, bromide, iodide, nitrate 4 and otheranions, if present, are reduced to negligible amounts.

The cation exchange resins are of the strong acid type, for example,sulfonic acids and salts. These include sulfonated polystyrene resins,sulfonated phenol-formaldehyde resins and other sulfonic acid types. Theanion exchange resins are of the strongly basic type, for example amineor quaternary salts. These include polystyrene-substituted quaternaryammonium salts, hydroxyalkyl quaternary type resins and other stronglybasic types.

The method of this invention is useful for purification of strongaqueous solutions up to 65 percent N H or higher. Dilute solutionshaving 5 percent or less of N H are also effectively purified when costscan be economically justified. It is preferred to purify hydrazinesolutions having from about I10 to 65 percent N H EXAMPLE I An aqueoussolution of hydrazine, containing 15 percent N H and 225 p.p.m. NaCl waspassed through a bed of sulfonated cation exchange resin and theeffluent was passed through a bed of strongly basic anion exchangeresin. The chloride content of the efiiuent was reduced to 20 ppm.

EXAMPLE II An aqueous solution of hydrazine containing 11.3 percent N Hand p.p.m. NaCl was passed successively through beds of strongly acidiccation exchange resin and strongly basic anion exchange resin. Nochlorides were detected in the first 45 gallons of efiiuent. A total of50 gallons of hydrazine was passed through the beds and this amounts to920 gallons per cubic foot of resin. The last of the efliuent containedonly 7 p.p.m. NaCl.

EXAMPLE III Aqueous hydrazine containing 13.9 percent N I-I and 72p.p.m. NaCl was passed successively through beds of strongly acidiccation exchange resin and strongly basic anion exchange resin. Thecation resin bed was 2 inches in diameter, 36 inches deep and contained0.0654 cu. ft. of bed. The anion resin bed was 2 inches in diameter, 48inches deep and contained 0.0874 cu. ft. of bed. The aqueous hydrazineflow averaged 245 milliliters per minute and the total throughput was94.9 gallons. The effluent, tested at intervals, averaged 6 p.p.m. NaCl.No change appeared in the hydrazine concentration.

EXAMPLE IV Using fresh resins, the procedure of Example III wasrepeated. The feed of aqueous hydrazine contained 73 to 83 p.p.m. NaCl.A total of 75.12 gallons of aqueous hydrazine was passed through thebeds. The product averaged 10.6 p.p.m. NaCl.

EXAMPLE V Using fresh resins, the procedure of Example III was repeated.The feed of aqueous hydrazine contained 50 to 78 p.p.m. NaCl. Theeffluent, amounting to 62.52 gallons, averaged 11.6 p.p.m. NaCl.

EXAMPLE VI Using fresh resins, the procedure of Example III wasrepeated. The feed of aqueous hydrazine contained 50 to 52 p.p.m. NaCl.The efiiuent, amounting to 93.18 gallons, averaged 6.6 p.p.m. NaCl.

EXAMPLE VII The cation resin bed had a diameter of 4.7 cm., a depth of60 cm. and a volume of 1041 cc. It was prepared by backwashing thecolumn upwards for 12 minutes with 353 cc./min. of deionized water,regenerating for 21 minutes at 139 cc./min. with 9 percent hydrochloricacid and rinsing for 60 minutes with 139 cc./min.

of deionized water. The bed was left covered with deionized water untilplaced in use.

The anion resin bed had a diameter of 4.7 cm., a depth of 70 cm. and avolume of 1215 cc. It was prepared by backwashing the column upwards for12 minutes with 353 cc./min. of deionized water, regenerating for 100minutes using 41.3 cc./rnin. of 4 percent aqueous caustic soda andrinsing for 160 minutes with 81.4 cc./ min. of deionized water. The bedwas left covered with deionized water until placed in use.

Aqueous hydrazine containing 35.5 percent N H 96 p.p.m. Na ion and 165C1 ion was passed serially through the bed of cation exchange resin andthe bed of anion exchange resin at a rate of 140 cc. per minute. Samplestaken every 30 minutes showed zero sodium and averaged 10.2 p.p.m.chloride.

EXAMPLE VIII The anion resin bed used in Example VII Was backwashedupwards for 12 minutes using 353 cc./min. of tap water, regenerated for30 minutes using 139 cc./min. of 9 percent HCl and rinsed for 70 minuteswith 158 cc./ min. of deionized water. The bed was left covered withdeionized water until used.

The anion resin bed used in Example VVII was backwashed for 15 minutesusing 230 cc./min. of tap water, regenerated for 80 minutes using 50cc./min. of a 4 percent aqueous caustic soda and rinsed for 210 minutesusing 87 cc./min. of deionized water. The bed was left covered withdeionized water until used.

Each column was purged with nitrogen for 30 minutes to remove air andwater. Then an aqueous solution of hydrazine containing 64.4 percent N H115 p.p.m. of Na ion and 130 p.p.m. of Cl ion was passed successivelythrough the resin beds of 242 cc./min. After 3 hours, the efiluentshowed 002 p.p.m. Na ion and 0.8 p.p.m. Cl ion.

EXAMPLE 1X Transmittance, percent at 490 mg.

Transmittance,

percent Na Ca C1", 490 p.p.m p.p.m. p.p.m mu.

What is claimed is:

1. A method of removing ionic impurities from an aqueous solution ofhydrazine by contacting said solution first with the hydroxyl form of astrongly basic anion exchange resin and separating from said anionexchange resin the first treated aqueous hydrazine, contacting saidfirst treated aqueous hydrazine with a strongly acidic cation exchangeresin in hydrazinium form and separating the'second treated aqueoushydrazine from said cation exchange resin.

2. The method as claimed 1 in which said cation exchange resin is asulfonated polystyrene resin.

3. The method as claimed in claim 1 in which said anion exchange resinis a polystyrene-substituted quaternary ammonium resin.

4. The method as claimed in claim 1 in which said aqueous solution ofhydrazine contains from 10 to percent N H 5. The method as claimed inclaim 1 in which said contacting is maintained at temperatures between 0and 300 F.

6. The method as claimed in claim 1 in which a flow of impure aqueoushydrazine is maintained through a first bed of said anion exchange resinand then through a first bed of said cation exchange resin until elutionof ions from said beds of ion exchange resin reaches a predeterminedlimit, transferring said flow of impure aqueous hydrazine through secondbeds of said resins, regenerating said first beds of resins while saidflow of aqueous hydrazine passes through said second beds of resins,transferring said flow of impure aqueous hydrazine to the regeneratedfirst beds and repeating the cycle.

References Cited UNITED STATES PATENTS 3,469,940 9/1969 Needham et al23-190 R Re. 24,213 9/1956 Blaricom et al. 260-22 R 2,789,036 4/ 1957Tillman 423-181 OSCAR R. VERTIZ, Primary Examiner H. S. MILLER,Assistant Examiner

